JP5752441B2 - Drive circuit, physical quantity detection device, angular velocity detection device, integrated circuit device, and electronic apparatus - Google Patents

Description

  The present invention relates to a drive circuit, a physical quantity detection device, an angular velocity detection device, an integrated circuit device, and an electronic apparatus.

  Various electronic devices such as digital cameras, navigation devices, and mobile phones are equipped with gyro sensors. Based on the angular velocity detected by the gyro sensor, processing such as camera shake correction, dead reckoning, and motion sensing is performed. .

  In recent years, downsizing of gyro sensors and high detection accuracy have been demanded, and as a gyro sensor that satisfies these requirements, for example, a vibration gyro sensor using a resonance phenomenon of a crystal resonator is widely used. In such a vibration gyro sensor, in order to realize high detection accuracy, it is effective to stabilize the oscillation of the vibrator by giving as much energy as possible to the vibrator. Therefore, in the conventional drive circuit, a rectangular wave drive signal obtained by amplifying a minute oscillation current output from the vibrator to the maximum is generated and fed back to the vibrator (Patent Documents 1 and 2).

JP 2008-14932 A JP 2008-64663 A

  However, since the rectangular-wave drive signal includes the odd-order harmonic components in addition to the resonance frequency component of the vibrator, these harmonic components cause other vibration modes as well as the original vibration mode of the vibrator. There is a possibility of excitation, and the detection accuracy may be deteriorated.

  This problem can be solved if a harmonic component is made small by adding a capacitor having a sufficient capacity to the drive terminal of the vibrator to smooth the edge of the drive signal. However, if the capacitance value of the capacitor is increased, the time required for the vibrator to oscillate stably increases, so the startup time required for the detection signal voltage to reach an appropriate level after the gyro sensor is turned on increases. A new problem arises.

  The present invention has been made in view of the above-described problems, and according to some aspects of the present invention, it is possible to shorten the time until the vibrator oscillates stably and to maintain stable oscillation. Possible drive circuits, physical quantity detection devices, angular velocity detection devices, integrated circuit devices, and electronic devices can be provided.

  (1) The present invention is a drive circuit that oscillates and drives a vibrator, a current-voltage conversion unit that converts an oscillation current of the vibrator that is input via a first signal line into a voltage, and the current voltage A drive signal generator for generating a drive signal for oscillating and driving the vibrator based on the signal converted into a voltage by the converter, and supplying the drive signal to the vibrator via a second signal line; An oscillation detection unit that detects whether the oscillation current has reached a predetermined value after the vibrator starts oscillating based on a signal converted into a voltage by a current-voltage conversion unit; and Based on the detection result, based on the detection result of the start-up oscillation unit that assists the oscillation operation of the vibrator until the oscillation current reaches the predetermined value, the first capacitor, and the oscillation detection unit, the oscillation current Until the predetermined value is reached. Disconnecting the capacitor from the second signal line, wherein after the oscillation current reaches the predetermined value; and a switch for connecting said first capacitor to said second signal line, a driving circuit.

  According to the present invention, the first capacitor is disconnected from the second signal line for supplying the drive signal to the vibrator until the oscillation current of the vibrator reaches a predetermined value, and the oscillation current of the vibrator is predetermined. After reaching the value, the first capacitor is connected. Therefore, the edge of the drive signal is steeper until the oscillation current of the vibrator reaches a predetermined value, and power can be supplied efficiently to the vibrator, reducing the time until the vibrator oscillates stably. can do. On the other hand, after the oscillation current of the vibrator reaches a predetermined value, the edge of the drive signal is lost and the harmonic component is reduced, so that stable oscillation of the vibrator can be maintained.

  (2) In this drive circuit, the first capacitor and the switch may be connected in series between the first signal line and the second signal line.

  (3) The drive circuit may further include a second capacitor connected to the second signal line.

  (4) In this drive circuit, the second capacitor may be connected between the first signal line and the second signal line.

  (5) The present invention is a physical quantity detection device including any one of the drive circuits described above and a vibrator driven to oscillate by the drive circuit.

  According to the present invention, it is possible to provide a physical quantity detection device capable of reducing the startup time from when the power is turned on until the physical quantity detection signal reaches a desired voltage level and capable of detecting the physical quantity with high accuracy.

  (6) The present invention is an angular velocity detection device including any one of the drive circuits described above.

  According to the present invention, it is possible to provide a physical quantity detection device capable of reducing the startup time from when the power is turned on until the angular velocity detection signal reaches a desired voltage level and capable of detecting the angular velocity with high accuracy.

  (7) The present invention is an integrated circuit device including any one of the drive circuits described above.

  (8) The present invention is an electronic device including any one of the drive circuits described above.

The functional block diagram of the angular velocity detection apparatus (an example of a physical quantity detection apparatus) of this embodiment. The top view of the vibration piece of a vibrator | oscillator. The figure for demonstrating operation | movement of a vibrator | oscillator. The figure for demonstrating operation | movement of a vibrator | oscillator. The figure which shows the structural example of a serial interface circuit. The figure which shows the structural example of a drive circuit. The figure which shows an example of the timing chart at the time of starting. The figure which shows the structural example of a detection circuit. The figure for demonstrating shortening of starting time. The functional block diagram of an electronic device.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. Also, not all of the configurations described below are essential constituent requirements of the present invention.

1. Physical quantity detection device In the following, a physical quantity detection device (angular velocity detection device) that detects an angular velocity as a physical quantity will be described as an example. However, the present invention detects one of various physical quantities such as angular velocity, angular acceleration, acceleration, and force. It is applicable to a device that can

  FIG. 1 is a functional block diagram of an angular velocity detection device (an example of a physical quantity detection device) according to this embodiment. An angular velocity detection device 1 according to the present embodiment includes a vibrator (sensor element) 100 and a signal processing IC (integrated circuit device) 2.

  The vibrator 100 is configured by sealing a vibrating piece in which a drive electrode and a detection electrode are arranged in a package (not shown). Generally, hermeticity in the package is secured in order to reduce the impedance of the resonator element as much as possible to increase the oscillation efficiency.

The vibrator 100 according to the present embodiment includes a resonator element formed of a Z-cut quartz substrate. The resonator element made of quartz is advantageous in that the detection accuracy of the angular velocity can be increased because the variation of the resonance frequency with respect to the temperature change is extremely small. However, the material of the resonator element of the vibrator 100 is not only quartz (SiO ₂ ), but also, for example, a piezoelectric single crystal such as lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), or lead zirconate titanate. A piezoelectric material such as a piezoelectric ceramic such as (PZT) may be used, or a silicon semiconductor may be used. For example, a structure in which a piezoelectric thin film such as zinc oxide (ZnO) or aluminum nitride (AlN) sandwiched between drive electrodes is arranged on a part of the surface of a silicon semiconductor may be used.

  In the present embodiment, the vibrator 100 is configured by a so-called double T-type vibrating piece having two T-type driving vibration arms. However, the resonator element of the vibrator 100 is not limited to the double T type, and may be, for example, a tuning fork type or a comb-teeth type, or a sound piece type having a shape such as a triangular prism, a quadrangular prism, or a cylindrical shape. Good.

  FIG. 2 is a plan view of the resonator element of the vibrator 100 according to the present embodiment. The X-axis, Y-axis, and Z-axis in FIG. 2 indicate crystal axes.

  As shown in FIG. 2, in the vibrating piece of the vibrator 100, the driving vibrating arms 101a and 101b extend from the two driving bases 104a and 104b in the + Y axis direction and the −Y axis direction, respectively. Here, the extending directions of the drive vibrating arms 101a and 101b may be within a range of ± 5 ° from the Y axis. Drive electrodes 112 and 113 are formed on the side surface and the upper surface of the drive vibration arm 101a, respectively, and drive electrodes 113 and 112 are formed on the side surface and the upper surface of the drive vibration arm 101b, respectively. The drive electrodes 112 and 113 are connected to the drive circuit 20 via the external output terminal 81 and the external input terminal 82 of the signal processing IC 2 shown in FIG.

  The drive bases 104a and 104b are connected to a rectangular detection base 107 via connecting arms 105a and 105b extending in the −X axis direction and the + X axis direction, respectively. Here, the extending directions of the connecting arms 105a and 105b may be within a range of ± 5 ° from the X axis.

  The detection vibrating arm 102 extends from the detection base 107 in the + Y axis direction and the −Y axis direction. Here, the extending direction of the detection vibrating arm 102 only needs to be within ± 5 ° from the Y axis. Detection electrodes 114 and 115 are formed on the upper surface of the detection vibrating arm 102, and a common electrode 116 is formed on the side surface of the detection vibrating arm 102. The detection electrodes 114 and 115 are connected to the detection circuit 30 via the external input terminals 83 and 84 of the signal processing IC 2 shown in FIG. The common electrode 116 is grounded.

  When an AC voltage is applied as a drive signal between the drive electrode 112 and the drive electrode 113 of the drive vibration arms 101a and 101b, the drive vibration arms 101a and 101b are as shown by an arrow B due to the inverse piezoelectric effect as shown in FIG. In addition, bending vibration (excitation vibration) in which the tips of the two drive vibration arms 101a and 101b repeat approach and separation from each other is performed.

  In this state, when an angular velocity with the Z axis as the rotation axis is applied to the resonator element of the vibrator 100, the driving vibration arms 101a and 101b are coriolis in a direction perpendicular to both the direction of the bending vibration of the arrow B and the Z axis. Gain power. As a result, the connecting arms 105a and 105b vibrate as indicated by an arrow C as shown in FIG. The detection vibrating arm 102 bends and vibrates as indicated by an arrow D in conjunction with the vibrations of the connecting arms 105a and 105b (arrow C). The phase of the bending vibration of the detection vibrating arm 102 and the bending vibration (excitation vibration) of the driving vibrating arms 101a and 101b due to the Coriolis force is shifted by 90 °.

  By the way, if the magnitude of the vibration energy or the magnitude of the vibration when the driving vibration arms 101a and 101b perform bending vibration (excitation vibration) is the same between the two driving vibration arms 101a and 101b, the driving vibration arms 101a and 101b, When the vibration energy of 101b is balanced and no angular velocity is applied to the vibrator 100, the detection vibrating arm 102 does not flex and vibrate. However, when the vibration energy balance between the two drive vibrating arms 101 a and 101 b is lost, bending vibration is generated in the detection vibrating arm 102 even when the angular velocity is not applied to the vibrator 100. This bending vibration is called leakage vibration, and is bending vibration indicated by an arrow D like the vibration based on the Coriolis force, but is in phase with the drive signal.

  Then, AC charges based on these bending vibrations are generated in the detection electrodes 114 and 115 of the detection vibration arm 102 by the piezoelectric effect. Here, the AC charge generated based on the Coriolis force changes according to the magnitude of the Coriolis force (in other words, the magnitude of the angular velocity applied to the vibrator 100). On the other hand, the AC charge generated based on the leakage vibration is constant regardless of the magnitude of the angular velocity applied to the vibrator 100.

  A rectangular weight portion 103 having a width wider than that of the drive vibrating arms 101a and 101b is formed at the ends of the drive vibrating arms 101a and 101b. By forming the weight portion 103 at the tips of the drive vibrating arms 101a and 101b, the Coriolis force can be increased and a desired resonance frequency can be obtained with a relatively short vibrating arm. Similarly, a weight portion 106 wider than the detection vibrating arm 102 is formed at the tip of the detection vibrating arm 102. By forming the weight portion 106 at the tip of the detection vibrating arm 102, the AC charge generated in the detection electrodes 114 and 115 can be increased.

  As described above, the vibrator 100 detects the AC charge (angular velocity component) based on the Coriolis force with the Z axis as the detection axis and the AC charge (vibration leakage component) based on the leakage vibration of the excitation vibration. Output via.

  Returning to FIG. 1, the signal processing IC 2 of this embodiment includes a power supply circuit 6, a reference voltage circuit 10, a drive circuit 20, a detection circuit 30, a serial interface circuit 40, a nonvolatile memory 50, an adjustment circuit 60, and a level determination circuit 70. It is configured to include. Note that the signal processing IC 2 of this embodiment may have a configuration in which some of these configurations (elements) are omitted or a new configuration (element) is added.

  The power supply circuit 6 is supplied with a power supply voltage VDD (for example, 3V) and a ground voltage VSS (0V) from the external input terminals 86 and 87, respectively, and generates a power supply voltage inside the signal processing IC2.

  The reference voltage circuit 10 generates a reference voltage 12 (for example, ½ VDD) from the power supply voltage supplied via the power supply circuit 6.

  The drive circuit 20 generates a drive signal 22 for exciting and vibrating the vibrator 100 and supplies the drive signal 22 to the drive electrode 112 of the vibrator 100 via the external output terminal 81. Further, the drive circuit 20 receives the oscillation current 24 generated in the drive electrode 113 by the excitation vibration of the vibrator 100 via the external input terminal 82, and the drive signal so that the amplitude of the oscillation current 24 is kept constant. The amplitude level of 22 is feedback controlled. Further, the drive circuit 20 generates a reference signal 26 of the synchronous detection circuit included in the detection circuit 30 and a clock signal 28 of the switched capacitor filter (SCF) circuit.

  The detection circuit 30 receives AC charges (detection currents) 32 and 34 generated at the detection electrodes 114 and 115 of the vibrator 100 via the external input terminals 83 and 84, respectively. Only the included angular velocity component is detected, a voltage level signal (angular velocity signal) 36 corresponding to the magnitude of the angular velocity is generated, and output to the outside via the external output terminal 88. The angular velocity signal 36 is A / D converted by a microcomputer (not shown) connected to the external output terminal 88, and used as various angular velocity data. Note that the signal processing IC 2 of this embodiment may include an A / D converter and output digital data representing the angular velocity to the outside via the serial interface circuit 40, for example.

  Thus, the drive circuit 20 and the detection circuit 30 function as the signal processing circuit 4 that performs signal processing on the vibrator 100.

  The adjustment circuit 60 selects either the adjustment data 52 or the adjustment data 42 according to the level determination signal 72 output from the level determination circuit 70, and the analog adjustment voltage 62 for the signal processing circuit 4 (drive circuit 20, detection circuit 30). (Offset compensation voltage, temperature compensation voltage, etc.) are generated. The adjustment circuit 60 is, for example, a D / A converter.

  The nonvolatile memory 50 holds various adjustment data 52 for the signal processing circuit 4 (the drive circuit 20 and the detection circuit 30), and can be configured as, for example, an EEPROM (Electrically Erasable Programmable Read-Only Memory).

  The serial interface circuit 40 has a two-line logic based on the clock signal 46 and the serial data signal 48 via the external input terminal 89 and the external input / output terminal 90 to write / read the adjustment data 52 to / from the nonvolatile memory 50, Processing for writing and reading adjustment data 42 and mode setting data 44 (not shown) is performed.

  FIG. 5 is a diagram illustrating a configuration example of the serial interface circuit 40. When data is written, the serial interface circuit 40 takes the serial data signal 48 input from the external input / output terminal 90 into the shift register 400 in synchronization with the clock signal 46 input from the external input terminal 89 and converts it into parallel data. Under the control of the read / write control circuit 410, the data is converted and written to any register (such as the adjustment register 422 or the mode setting register 424) included in the nonvolatile memory 50 or the internal register group 420. On the other hand, at the time of data reading, under the control of the read / write control circuit 410, the data stored in the nonvolatile memory 50 or the data stored in any of the registers included in the internal register group 420 is transferred to the shift register. 400 is parallel loaded, the data of the shift register 400 is shifted in synchronization with the clock signal 46 input from the external input terminal 89, and the serial data signal 48 is output from the external input / output terminal 90.

  In order to write data to the nonvolatile memory 50, it is necessary to supply energy sufficient to invert the data held in the memory element. Therefore, as shown in FIG. 1, a high power supply voltage VPP (for example, 15 V or more) is supplied to the nonvolatile memory 50 via the external input terminal 85 when data is written.

  In the present embodiment, data is written into the nonvolatile memory 50 only when the angular velocity detection device 1 is assembled, inspected, evaluated, analyzed, etc., and is used in the nonvolatile memory 50 when used in the market. The writing of data is prohibited. Therefore, when the angular velocity detection device 1 is used in the market, the external input terminal 85 is set to open. Thereby, the voltage VPP of the external input terminal 85 becomes substantially equal to VDD through the pull-up resistor 92, and erroneous writing can be prevented.

  The adjustment data 52 is written in the non-volatile memory 50, for example, at the time of final inspection after assembly of the angular velocity detection device 1. Specifically, the adjustment value is written in the adjustment register 422 included in the internal register group of the serial interface circuit 40, and the signal processing circuit 4 (drive circuit) is used by using the adjustment value (adjustment data 42) written in the adjustment register 422. 20, the operation of the detection circuit 30) is confirmed. While changing the adjustment value, the signal processing circuit 4 (the drive circuit 20 and the detection circuit 30) determines an optimum adjustment value for performing a desired operation, and the optimum adjustment value is non-volatile once as the adjustment data 52. Write to memory 50. In this way, the inspection time can be shortened, and a decrease in reliability due to application of a high power supply voltage during data writing can be minimized.

  In order to realize such an adjustment method, it is necessary for the adjustment circuit 60 to be able to select which adjustment data of the nonvolatile memory 50 or the adjustment register 422 is used. Therefore, in this embodiment, the level determination circuit 70 determines the voltage level of VPP, and VPP is a predetermined voltage value V1 (for example, 8V) higher than VDD or a predetermined voltage value V2 (for example, 1/2 VDD) that is lower than VDD. A level determination signal 72 indicating whether the voltage value is the following voltage value or the voltage value VPP is higher than V2 and lower than V1 is generated. The adjustment circuit 60 selects the adjustment data 42 in the internal register when VPP ≧ V1 or VPP ≦ V2 according to the level determination signal 72, and the adjustment data in the nonvolatile memory 50 when V2 <VPP <V1. 52 is selected.

  As described above, when the angular velocity detection device 1 is used in the market, the external input terminal 85 is set to be open, so that the VPP becomes substantially equal to VDD by the pull-up resistor 92, and the adjustment data 52 is always supplied by the adjustment circuit 60. Is selected. On the other hand, when the angular velocity detection device 1 is assembled, inspected, evaluated, analyzed, etc., the adjustment data 42 is supplied to the adjustment circuit 60 by applying a voltage of V1 or higher or a voltage of V2 or lower (for example, 0 V) to the external input terminal 85. Can also be selected.

  In the present embodiment, the setting value of the mode setting register 424 is rewritten to use the normal operation mode (mode 1) used in the market or the assembly, inspection, evaluation, analysis, etc. of the angular velocity detection device 1. One of the operation modes (mode 2) can be selected. For example, if the set value of the 5-bit mode setting register 424 is “00000”, the mode 1 is selected, and if any of “00001” to “11111” is set, the mode 2 is selected. Mode 2 is subdivided according to each set value of “00001” to “11111”, and a node to be monitored is selected according to the set value for the signal processing circuit 4 (drive circuit 20, detection circuit 30). Or change the connection relationship.

  In this embodiment, in order to ensure reliability in the market, only mode 1 is possible, and rewriting to mode 2 is prohibited, and mode 1 or mode 2 is set only when the angular velocity detection device 1 is assembled, inspected, evaluated, or analyzed. to enable. In order to realize this, rewriting of the setting value of the mode setting register 424 is enabled only when VPP ≧ V1 or VPP ≦ V2, and is disabled otherwise. Therefore, in this embodiment, the level determination signal 72 is supplied to the asynchronous reset terminal of the mode setting register 424. As a result, when VPP ≧ V1 or VPP ≦ V2, the setting value of the mode setting register 424 is reset to “00000” to become mode 1 and rewriting becomes invalid, and when V2 <VPP <V1, the mode setting register The rewriting of the set value of 424 becomes effective.

  In the present embodiment, in particular, not only when VPP ≧ V1 but also when VPP ≦ V2, the adjustment data 42 is selected by the adjustment circuit 60 and the rewriting of the setting value of the mode setting register 424 is enabled. Thus, there is an advantage that the angular velocity detection device 1 can be evaluated and analyzed even in an environment where there is no power supply device that generates a high voltage.

  Next, the drive circuit 20 will be described. FIG. 6 is a diagram illustrating a configuration example of the drive circuit 20. As shown in FIG. 6, the drive circuit 20 of this embodiment includes an I / V conversion circuit (current / voltage conversion circuit) 200, a high-pass filter (HPF) 210, a comparator 212, capacitors 214 and 216, a switch 218, and an RC filter. 220, amplifier 230, full-wave rectifier circuit 240, subtractor 250, integrator 252, pull-up resistor 254, comparator 260, buffer circuit 262, oscillation detection circuit 270, start-up oscillation circuit 280, switch 282, inverter circuit (inverted logic) Circuit) 290. Note that the drive circuit 20 of this embodiment may have a configuration in which some of these configurations (elements) are omitted or a new configuration (element) is added.

The drive current that has flowed through the resonator element of the vibrator 100 is converted into an AC voltage signal by the I / V conversion circuit 200. In the I / V conversion circuit 200 of this embodiment, a resistor 204 is connected between an inverting input terminal (−input terminal) and an output terminal of an operational amplifier 202, and a non-inverting input terminal (+ input terminal) of the operational amplifier 202 is an analog ground. It is the structure connected to. The output voltage V _IV of the I / V conversion circuit 200 is expressed by the following equation (1), where i is the oscillation current of the vibrator 100 and R is the resistance value of the resistor 204.

The output signal of the I / V conversion circuit 200 is input to the comparator 212 after the offset is canceled by the high pass filter 210. The comparator 212 amplifies the voltage of the input signal and outputs a binarized signal (square wave voltage signal). However, in this embodiment, the comparator 212 is an open drain output comparator that can output only a low level, and the high level is pulled up to the output voltage of the integrator 252 via the pull-up resistor 254. The binarized signal output from the comparator 212 is supplied as the drive signal 22 to the drive electrode 112 of the resonator element of the vibrator 100 via the external output terminal 81. By making the frequency of the drive signal 22 (drive frequency f _d ) coincide with the resonance frequency of the vibrator 100, the vibrator 100 can be stably oscillated.

  Further, in the present embodiment, the amplitude of the drive signal 22 is adjusted so that the oscillation current of the vibrator 100 is constant, that is, the level of the output voltage of the I / V conversion circuit 200 is constant. By doing so, the vibrator 100 can be oscillated extremely stably, and the angular velocity detection accuracy can be improved.

  However, the resistance value R of the resistor 204 included in the I / V conversion circuit 200 varies about ± 20% with respect to the design value for each IC due to manufacturing variations. The conversion rate to the output voltage of the / V conversion circuit 200 varies from IC to IC. Therefore, when the amplitude of the drive signal 22 is adjusted so that the output voltage of the I / V conversion circuit 200 becomes a constant design value, the oscillation current of the vibrator 100 differs for each IC. As a result, an IC with a larger deviation of the oscillation current from the design value can be a factor that degrades the angular velocity detection accuracy and detection sensitivity.

  Further, since the temperature characteristic of the resistance value of the resistor 204 is not flat, the output voltage of the I / V conversion circuit 200 fluctuates due to the influence of the resistor 204 even if the oscillation current of the vibrator 100 is constant. End up. As a result, the oscillating current of the vibrator 100 fluctuates according to the temperature, which can be a factor that degrades the angular velocity detection accuracy and detection sensitivity. Similarly, manufacturing variations and temperature fluctuations in capacitance values of capacitors 304 and 314 that are components of charge amplifiers 300 and 310 included in the detection circuit 30 described later can also be a factor that degrades angular velocity detection accuracy and detection sensitivity.

  Therefore, in the present embodiment, the RC filter 220 is provided for the purpose of canceling the variation of the resistance value of the resistor 204 and the capacitance value of the capacitors 304 and 314 and the temperature fluctuation, and suppressing the deterioration of the detection accuracy and detection sensitivity of the angular velocity, The output signal of the I / V conversion circuit 200 is passed through the RC filter 220. The reason why the deterioration of the detection accuracy and detection sensitivity of the angular velocity can be suppressed by providing the RC filter 220 will be described later in the description of the detection circuit 30.

The RC filter 220 includes a resistor 222 and a capacitor 224, and functions as a primary low-pass filter. That is, assuming that the resistance value of the resistor 222 is R ₁ and the capacitance value of the capacitor 224 is C ₁ , the transfer function of the RC filter 220 is expressed by the following equation (2).

  From the equation (2), the frequency characteristic of the voltage gain of the RC filter 220 is expressed by the following equation (3).

In the present embodiment, R ₁ and C ₁ are selected so that (ω _d · C ₁ · R ₁ ) ² >> _{1 with} respect to the oscillation angular frequency ω _d (= 2πf _d ) of the vibrator 100. In this case, the output voltage V _RC of the RC filter 220 is expressed by the following equation (4) from the equations (1) and (3).

  Further, from the equation (2), the frequency characteristic of the phase of the RC filter 220 is expressed by the following equation (5).

Therefore, according to the equation (5), the output signal (angular frequency: ω _d ) of the I / V conversion circuit 200 passes through the RC filter 220, so that the phase is θ = arctan (ω _d · C ₁ · R ₁ ). Is delayed. That is, the RC filter 220 also functions as a phase shift circuit. For example, if ω _d = 2π × 50 kHz (f _d = 50 kHz) and C ₁ · R ₁ = 1 / (2π × 5 kHz), then θ≈84 °.

However, from the equation (4), the output signal (angular frequency: ω _d ) of the I / V conversion circuit 200 passes through the RC filter 220, so that the amplitude is about 1 / (ω _d · C ₁ · R ₁ ). Attenuates twice. For example, when ω _d = 2π × 50 kHz (f _d = 50 kHz) and C ₁ · R ₁ = 1 / (2π × 5 kHz), the amplitude of the output signal of the RC filter 220 is the output signal of the I / V conversion circuit 200. Is about 1/10 of the amplitude of. Therefore, in the present embodiment, in order to facilitate signal processing in a circuit subsequent to the RC filter 220, a voltage correction amplifier 230 that amplifies the output signal of the RC filter 220 (for example, the input signal is represented by ω _d · C _An amplifier that amplifies ₁ · R ₁ time) is added. However, the amplifier 230 may not be added if a circuit subsequent to the RC filter 220 can directly process the output signal of the RC filter 220.

  The output signal of the amplifier 230 is input to the full-wave rectifier circuit 240 and full-wave rectified.

The output signal (full-wave rectified signal 242) of the full-wave rectifier circuit 240 is input to the subtractor 250, subjected to voltage subtraction processing with the reference voltage 12, and then integrated by the integrator 252. The output voltage of the integrator 252 decreases as the amplitude of the output signal of the I / V conversion circuit 200 increases. Since the high level of the drive signal 22 is pulled up to the output voltage of the integrator 252 via the pull-up resistor 254, the amplitude V _DR of the drive signal 22 is inversely proportional to the output voltage V _RC of the RC filter 220. From Equation (4), it is expressed by the following Equation (6) using an appropriate coefficient A.

  With such a configuration, the amplitude level of the drive signal 22 is feedback-controlled so that the amplitude of the oscillation current 24 of the vibrator 100 is kept constant.

  However, immediately after the power is turned on, the oscillation of the vibrator 100 is stopped, and in order for such feedback control to be performed promptly, the oscillation of the vibrator 100 is started and assistance is made until the oscillation operation is stabilized. There is a need to. Therefore, in the present embodiment, an oscillation detection circuit 270, a startup oscillation circuit 280, and a switch 282 are provided.

  The start-up oscillation circuit 280 is an oscillation circuit that self-oscillates at a frequency close to the resonance frequency of the vibrator 100 and assists the oscillation operation of the vibrator 100. The startup oscillation circuit 280 can be realized by, for example, a CR oscillation circuit.

Oscillation detection circuit 270, the voltage level of the output signal of the full-wave rectifier circuit 240 (full wave rectified signal 242) is compared with a predetermined threshold, to a voltage level of the full-wave rectified signal 242 reaches a predetermined threshold value V ₁ ( The oscillation operation of the startup oscillation circuit 280 is continued until the oscillation current reaches a predetermined value. When the voltage level of the full-wave rectification signal 242 reaches the threshold value V ₁ (when the oscillation current 24 reaches the predetermined value), the startup oscillation circuit 280 The oscillation operation of is stopped. The oscillation detection circuit 270 until the voltage level of the full-wave rectified signal 242 reaches the threshold V ₁ (oscillation current 24 reaches a predetermined value) turns on the switch 282, the voltage level of the full-wave rectified signal 242 Once you reach the threshold value V ₁ (oscillation current if reaches the predetermined value) generates a switch control signal 272 for turning off the switch 282.

As shown in FIG. 7, when the power is turned on, VDD changes from 0 V to the power supply voltage V ₀ , but the oscillation of the vibrator 100 stops immediately after the power is turned on, so the voltage level of the full-wave rectified signal 242 is 0 V. is there. Therefore, the startup oscillation circuit 280 performs an oscillation operation and the switch 282 is turned on, and the oscillation frequency component of the startup oscillation circuit 280 is superimposed on the output signal of the high-pass filter (HPF) 210. The drive signal 22 including the oscillation frequency component of the start-up oscillation circuit 280 is supplied to the vibrator 100, and the vibrator 100 starts to oscillate. Then, the oscillation current 24 of the vibrator 100 is gradually increased, when it as exceeds the threshold value V ₁ becomes higher voltage level of the full-wave rectified signal 242, the switch 282 together with the oscillating operation is stopped in the start oscillator 280 Turn off. Thereafter, when the voltage level of the full-wave rectified signal 242 reaches a desired voltage value V ₂ , the voltage level of the full-wave rectified signal 242 is held at V ₂ (that is, the amplitude of the oscillation current 24 of the vibrator 100). The amplitude level of the drive signal 22 is feedback controlled (so that is held at a desired value). Hereinafter, the time from immediately after power-on until the voltage level of the full-wave rectified signal 242 reaches the threshold V ₁ is referred to as "oscillation wait time".

Incidentally, in the state in which the vibrator 100 is oscillating, the comparator 212 is outputting a rectangular wave signal of a frequency f _d obtained by binarizing the output signal of the high pass filter 210, the rectangular wave signal, the f _d Odd-order frequency components (3f _d , 5f _d , 7f _d ,...) Are also included. Therefore, when this rectangular wave signal is supplied as it is to the vibrator 100 as the drive signal 22, any one of the frequency components 3f _d , 5f _d , 7f _d ,... Coincides with the vibration mode of the vibrator 100 and is unnecessary. Vibration component may be generated. This unnecessary vibration component prevents stable oscillation of the vibrator 100, and if this unnecessary vibration component is detected by the detection circuit 30, the detection accuracy of the angular velocity is deteriorated.

Therefore, in this embodiment, by rounding the edge of the drive signal 22 for the purpose of reducing the odd-order frequency components of f _d, it is provided a capacitor 214 and a capacitor 216 to the inside of the drive circuit 20. The capacitor 214 is connected between a signal line (second signal line) that supplies the drive signal 22 to the vibrator 100 and a signal line (first signal line) to which the oscillation current 24 is input from the vibrator 100. ing. On the other hand, the capacitor 216 is connected between the first signal line and the second signal line via the switch 218. The on / off of the switch 28 is controlled by a switch control signal 292 obtained by logically inverting the switch switching signal 272 by the inverter circuit 290. Accordingly, the switch 218 is turned off when the switch 282 is on, and the switch 218 is turned on when the switch 282 is off.

In short, as shown in FIG. 7, the switch 218 is turned off until the oscillation waiting time elapses, and only the capacitor 214 is connected between the first signal line and the second signal line. The switch 218 is turned on, and capacitors 214 and 216 are connected in parallel between the first signal line and the second signal line. For example, if the capacitors 214 and 216 have capacitances C ₁ and C ₂ , respectively, the capacitance between the first signal line and the second signal line is C ₁ until the oscillation waiting time elapses. Thus, after the oscillation waiting time elapses, it increases to C ₁ + C ₂ .

  As the load capacity of the second signal line is increased, the edge of the drive signal 22 becomes dull and unnecessary vibration components are reduced, so that the oscillation operation of the vibrator 100 can be further stabilized. On the other hand, as the edge of the drive signal 22 is steeper, power can be supplied more efficiently to the vibrator 100, so that the oscillation waiting time can be shortened. Therefore, in this embodiment, the switch 218 is switched from OFF to ON before and after the oscillation waiting time elapses, thereby reducing both the oscillation waiting time of the vibrator 100 and maintaining stable oscillation.

Since the load capacity of the second signal line may be switched, a capacitor 214 is connected between the second signal line and the ground, and a switch 218 is connected between the second signal line and the ground. A capacitor 216 may be connected. Further, the capacitor 214 may be removed, and the capacity of the capacitor 216 may be increased to C ₁ + C ₂ .

The drive circuit 20 of the present embodiment is further provided with a comparator 260 that amplifies the output signal of the high-pass filter 210 and outputs a binarized signal (square wave voltage signal). The reference signal 26 of the synchronous detection circuit included in the detection circuit 30 is used. Frequency of the reference signal 26 is equal to the drive frequency f _d. Since the output signal of the comparator 212 fluctuates at a high level, if the high level does not exceed the logic threshold value in the synchronous detection circuit, a malfunction occurs. Therefore, the comparator 260 is not used as a reference signal. Separately provided.

The output signal of the comparator 260 is input to the buffer circuit 262, and the output signal of the buffer circuit 262 is supplied to the SCF circuit included in the detection circuit as the clock signal 28 (frequency: f _d ).

  Next, the detection circuit 30 will be described. FIG. 8 is a diagram illustrating a configuration example of the detection circuit 30. As shown in FIG. 8, the detection circuit 30 of this embodiment includes charge amplifiers 300 and 310, a differential amplifier 320, a high-pass filter (HPF) 322, an amplifier 324, a synchronous detection circuit 326, a variable gain amplifier 328, and a switched capacitor filter. (SCF) 330 and an output buffer 332 are included. Note that the detection circuit 30 of the present embodiment may have a configuration in which some of these configurations (elements) are omitted or a new configuration (element) is added.

  An AC charge (detection current) 32 including an angular velocity component and a vibration leakage component is input to the charge amplifier 300 from the detection electrode 114 of the vibration piece of the vibrator 100 via the external input terminal 83. Similarly, AC charge (detection current) 34 including an angular velocity component and a vibration leakage component is input to the charge amplifier 310 from the detection electrode 115 of the resonator element of the vibrator 100 via the external input terminal 84.

  In the charge amplifier 300 of this embodiment, a capacitor 304 is connected between an inverting input terminal (−input terminal) and an output terminal of the operational amplifier 302, and a non-inverting input terminal (+ input terminal) of the operational amplifier 302 is connected to an analog ground. It is a configuration. Similarly, in the charge amplifier 310 of this embodiment, a capacitor 314 is connected between the inverting input terminal (−input terminal) and the output terminal of the operational amplifier 312, and the non-inverting input terminal (+ input terminal) of the operational amplifier 312 is analog ground. It is the structure connected to. The capacitance values of the capacitors 304 and 314 are set to the same value. The charge amplifiers 300 and 310 convert the input AC charges (detection currents) 32 and 34, respectively, into AC voltage signals. The AC charge (detection current) 32 input to the charge amplifier 300 and the AC charge (detection current) 34 input to the charge amplifier 310 are 180 degrees out of phase with each other, and the output signal of the charge amplifier 300 and the output signal of the charge amplifier 310 Are in opposite phases (shifted by 180 °).

The output voltage V _CA1 of the charge amplifier 300 is expressed by the following equation (7), where i _{1 is} the detection current 32, ω _{1 is} the angular frequency of the detection current 32, and C is the capacitance value of the capacitor 304.

The output voltage V _CA2 of the charge amplifier 310 is expressed by the following equation (8) because the detection current 34 is −i ₁ , the frequency of the detection current 34 is ω ₁ , and the capacitance value of the capacitor 314 is C.

Here, since i ₁ is proportional to the amplitude V _DR of the drive signal 22, from equations (6), (7), and (8), V _CA1 and V _CA2 are respectively determined using an appropriate coefficient B. It represents with Formula (9) and Formula (10).

The differential amplifier 320 differentially amplifies the output signal of the charge amplifier 300 and the output signal of the charge amplifier 310. The differential amplifier 320 cancels the in-phase component and adds and amplifies the anti-phase component. The output voltage V _DF of the differential amplifier 320 is expressed by the following equation (11) from the equations (9) and (10) when the gain of the differential amplifier 320 is 1.

From the equation (11), in the output signal of the differential amplifier 320, the manufacturing variation and the temperature variation of the resistance value R of the resistor 204 of the I / V conversion circuit 200 described above are the resistance value R ₁ of the resistor 222 of the RC filter 220. It will be canceled due to manufacturing variations and temperature fluctuations. The same manner, manufacturing variations and temperature variation in the capacitance value C of the capacitor 314 of the capacitor 304 and charge amplifier 310 of the charge amplifier 300 is canceled by the manufacturing variations and temperature variation in the capacitance value _{C 1} of the capacitor 224 of the RC filter 220 It will be. As a result, it is possible to suppress deterioration in detection accuracy and detection sensitivity of the angular velocity.

  The high pass filter 322 cancels the DC component included in the output signal of the differential amplifier 320.

  The amplifier 324 outputs an AC voltage signal obtained by amplifying the output signal of the high pass filter 322.

  The synchronous detection circuit 326 synchronously detects an angular velocity component included in the output signal of the amplifier 324 using the binarized signal output from the comparator 260 included in the drive circuit 20 as a reference signal 26. For example, the synchronous detection circuit 326 selects the output signal of the amplifier 324 as it is when the reference signal 26 is at a high level, and inverts the output signal of the amplifier 324 with respect to the reference voltage 12 when the reference signal 26 is at a low level. It can be configured as a circuit for selecting a signal.

  The output signal of the amplifier 324 includes an angular velocity component and a vibration leakage component. The angular velocity component has the same phase as the reference signal 26, whereas the vibration leakage component has an opposite phase. Therefore, the angular velocity component is synchronously detected by the synchronous detection circuit 326, but the vibration leakage component is not detected.

  The variable gain amplifier 328 amplifies or attenuates the output signal of the synchronous detection circuit 326 and outputs a signal having a desired voltage level. The output signal of the variable gain amplifier 328 is input to the switched capacitor filter (SCF) circuit 330.

The SCF circuit 330 functions as a low-pass filter that removes a high-frequency component contained in the output signal of the variable gain amplifier 328 and passes a signal in a frequency range determined by specifications. The frequency characteristic of the SCF circuit 330 (low-pass filter) is determined by the frequency ratio f _d of the clock signal 28 obtained by stable oscillation of the vibrator 100 and the capacitance ratio of the capacitor (not shown). There is an advantage that variation in frequency characteristics is extremely small.

  The output signal of the SCF circuit 330 is buffered by the output buffer 332 and amplified or attenuated to a signal having a desired voltage level as necessary. The output signal of the output buffer 326 is a signal having a voltage level corresponding to the angular velocity, and is output to the outside as the angular velocity signal 36 via the external output terminal 88 of the signal processing IC 2.

In the angular velocity detection device 1 having such a configuration, as described above, the oscillation waiting time can be shortened by turning off the switch 218 of the drive circuit 20 until the oscillation waiting time of the vibrator 100 elapses after the power is turned on. it can. Since the oscillation waiting time of the vibrator 100 is shortened, the time until the detection currents 32 and 34 output from the vibrator 100 are stabilized is also shortened. As a result, as shown in FIG. After the input, the startup time until the angular velocity signal 36 reaches a desired voltage level (for example, near the reference voltage Vref if the angular velocity detection device 1 is stationary) is shortened from t ₂ to t ₁ . Note that the waveform indicated by the broken line of the angular velocity signal 36 in FIG. 9 indicates stable oscillation of the vibrator 100 when the switch 218 is always on, that is, between the first signal line and the second signal line. This is a waveform when the capacity C ₁ + C ₂ necessary for maintaining is always connected, and the activation time in this case is t ₂ .

  On the other hand, after the oscillation waiting time of the vibrator 100 has elapsed, the stable oscillation of the vibrator 100 can be continued by turning on the switch 218 of the drive circuit 20. As a result, high detection accuracy can be maintained after stable oscillation of the vibrator 100.

  Thus, according to the angular velocity detection device 1 of the present embodiment, it is possible to detect the angular velocity with high accuracy while reducing the activation time.

  The drive circuit 20 in the present embodiment corresponds to the drive circuit in the present invention. The I / V conversion circuit 200 corresponds to a “current / voltage conversion unit” in the present invention. The configuration of the high pass filter 210 and the comparator 212 corresponds to the “drive signal generation unit” in the present invention. The oscillation detection circuit 270 corresponds to an “oscillation detection unit” in the present invention. The startup oscillation circuit 280 corresponds to a “startup oscillation unit” in the present invention. The capacitor 216 corresponds to the “first capacitor” in the present invention. The switch 218 corresponds to the “switch” in the present invention. The capacitor 214 corresponds to a “second capacitor” in the present invention.

2. Electronic Device FIG. 10 is a functional block diagram illustrating a configuration example of the electronic device of the present embodiment. The electronic device 500 of this embodiment includes a signal generation unit 600, a CPU 700, an operation unit 710, a display unit 720, a ROM (Read Only Memory) 730, a RAM (Random Access Memory) 740, and a communication unit 750. . Note that the electronic device of this embodiment may have a configuration in which some of the components (each unit) in FIG. 10 are omitted or other components are added.

  The signal generation unit 600 includes a drive circuit 610, generates a given signal according to the control of the CPU 700, and outputs it to the CPU 700. The drive circuit 610 performs a process of oscillating and driving a vibrator (not shown).

  The CPU 700 performs various calculation processes and control processes in accordance with programs stored in the ROM 730. Specifically, the CPU 700 controls the signal generation unit 600 or receives a signal generated by the signal generation unit 600 and performs various calculation processes. In addition, the CPU 700 uses the communication unit 750 to perform various processes in accordance with operation signals from the operation unit 710, to transmit display signals for displaying various types of information on the display unit 720, and to perform data communication with the outside. Performs control processing and the like.

  The operation unit 710 is an input device including operation keys, button switches, and the like, and outputs an operation signal corresponding to an operation by the user to the CPU 700.

  The display unit 720 is a display device configured by an LCD (Liquid Crystal Display) or the like, and displays various types of information based on a display signal input from the CPU 700.

  The ROM 730 stores programs for the CPU 700 to perform various calculation processes and control processes, various programs and data for realizing predetermined functions, and the like.

  The RAM 740 is used as a work area of the CPU 700, and temporarily stores programs and data read from the ROM 730, data input from the operation unit 710, calculation results executed by the CPU 700 according to various programs, and the like.

  The communication unit 750 performs various controls for establishing data communication between the CPU 700 and an external device.

  By incorporating the drive circuit of this embodiment (the drive circuit 20 in FIG. 1) in the electronic device 500 as the drive circuit 610, both high-precision processing and reduction in processing time can be achieved.

  Note that various electronic devices can be considered as the electronic device 500, such as a digital still camera, a video camera, a navigation device, a vehicle body posture detection device, a pointing device, a game controller, a mobile phone, and a head mounted display (HMD). It is done.

  In addition, this invention is not limited to this embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention.

  For example, the excitation means for driving vibration of the vibrator (sensor element) and the detection means for detection vibration are not only based on the piezoelectric effect described in the present embodiment, but also an electrostatic type using electrostatic force (Coulomb force), A Lorentz type using magnetic force may be used.

  For example, when the high level of the drive signal 22 does not exceed the logical threshold value in the synchronous detection circuit 326, a signal obtained by buffering the drive signal 22 may be used as the clock signal 28 of the SCF circuit 330.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 Angular velocity detection apparatus, 2 Signal processing IC (integrated circuit apparatus), 4 Signal processing circuit, 6 Power supply circuit, 10 Reference voltage circuit, 20 Drive circuit, 22 Drive signal, 24 Oscillation current, 26 Reference signal, 27 Switching control signal, 28 clock signal, 30 detection circuit, 32, 34 AC charge (detection current), 36 angular velocity signal, 40 serial interface circuit, 42 adjustment data, 44 mode setting data, 46 clock signal, 48 serial data signal, 50 nonvolatile memory, 52 adjustment data, 60 adjustment circuit, 62 analog adjustment voltage, 70 level determination circuit, 72 level determination signal, 81 external output terminal, 82, 83, 84, 85, 86, 87 external input terminal, 88 external output terminal, 89 external Input terminal, 90 External input / output terminal, 92 Pull-up resistor, 00 vibrator, 101a to 101b drive vibration arm, 102 detection vibration arm, 103 weight part, 104a to 104b drive base, 105a to 105b connection arm, 106 weight part, 107 detection base, 112 to 113 drive electrode, 114 to 115 detection electrode, 116 common electrode, 200 I / V conversion circuit (current-voltage conversion circuit), 202 operational amplifier, 204 resistance, 210 high pass filter (HPF), 212 comparator, 214, 216 capacitor, 218 switch, 220 RC filter, 222 resistor, 224 capacitor, 230 amplifier, 240 full-wave rectifier circuit, 242 full-wave rectified signal, 250 subtractor, 252 integrator, 254 pull-up resistor, 260 comparator, 262 buffer circuit, 270 oscillation detection circuit, 272 Switch control signal, 280 start-up oscillation circuit, 282 switch, 290 inverter circuit (inverted logic circuit), 292 switch control signal, 300 charge amplifier, 302 operational amplifier, 304 capacitor, 310 charge amplifier, 312 operational amplifier, 314 capacitor, 320 differential Amplifier, 322 High-pass filter (HPF), 324 Amplifier, 326 Synchronous detection circuit, 328 Variable gain amplifier, 330 Switched capacitor filter (SCF), 332 Output buffer, 500 Electronic device, 600 Signal generator, 610 Drive circuit, 700 CPU, 710 operation unit, 720 display unit, 730 ROM, 740 RAM, 750 communication unit

Claims (8)

A drive circuit for oscillating and driving a vibrator,
A current-voltage converter that converts the oscillation current of the vibrator input via the first signal line into a voltage;
A drive signal generator that generates a drive signal for oscillating and driving the vibrator based on the signal converted into a voltage by the current-voltage converter, and supplies the drive signal to the vibrator via a second signal line When,
Based on the signal converted into voltage by the current-voltage converter, an oscillation detector that detects whether or not the oscillation current has reached a predetermined value after the vibrator starts oscillating;
Based on the detection result of the oscillation detection unit, a start-up oscillation unit that assists the oscillation operation of the vibrator by self-oscillation until the oscillation current reaches the predetermined value;
A first capacitor;
Based on the detection result of the oscillation detection unit, the first capacitor is disconnected from the second signal line until the oscillation current reaches the predetermined value, and after the oscillation current reaches the predetermined value, the first capacitor is disconnected. And a switch for connecting one capacitor to the second signal line. In claim 1,
The drive circuit, wherein the first capacitor and the switch are connected in series between the first signal line and the second signal line. In claim 1 or 2,
The drive circuit further comprising a second capacitor connected to the second signal line. In claim 3,
The second capacitor is
A drive circuit connected between the first signal line and the second signal line. A drive circuit according to any one of claims 1 to 4,
A physical quantity detection device including a vibrator driven to oscillate by the drive circuit. In any one of claims 1 to 4 comprising a driving circuit according angular velocity detecting device. In any one of claims 1 to 4 comprising a driving circuit according an integrated circuit device. In any one of claims 1 to 4 comprising a driving circuit according an electronic device.

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